there is also alot of marketing done. to get an even % means the line must be bred to be stable , even then there will genetic drift. ive learned clones are the only way to get close to what you expect your buying. its a carnivourous market and even when a breeder grows lets say 100 cultivars and hits it big on 1 , they exploit the test results of that 1 cultivar and use it to brand the line. they also probably only test the best tops with the highest amount of thc(duh) . people like data Nd whatnot so telling them they will get 24-29% makes them spend cash faster. plus alot of us are not able to get our product tested at all, or use cheap test kits that average over a few % in a range.
in the end I agree with
@PadawanWarrior that they are destroying the gene pool and with everything it will make it worse.
edit: I would say though that mephisto is probably one of the leading autoflower breeders, and rocbudinc? but if they are smart in their breeder tactics they won't lower the thc but keep it on the rise